TOKYO (AP) — Japan's population of 128 million will shrink by one-third and seniors will account for 40 percent of people by 2060, placing a greater burden on a smaller working-age population to support the social security and tax systems.

The grim estimate of how rapid aging will shrink Japan's population was released Monday by the Health and Welfare Ministry.

In year 2060, Japan will have 87 million people. The number of people 65 or older will nearly double to 40 percent, while the national work force of people between ages 15 and 65 will shrink to about half of the total population, according to the estimate, made by the National Institute of Population and Social Security Research.

The total fertility rate, or the expected number of children born per woman during lifetime, in 2060 is estimated at 1.35, down from 1.39 in 2010 — well below more than 2 needed to keep the country's population from declining. But the average Japanese will continue to live longer. The average life expectancy for 2060 is projected at 90.93 for women, up from 86.39 in 2010, and 84.19 years for men, up from 79.64 years.

Prime Minister Yoshihiko Noda has pledged to push for social security and tax reforms this year. A bill he promised to submit by the end of March would raise the 5 percent sales tax in two stages to 8 percent in 2014 and 10 percent by 2015, although opposition lawmakers and the public pose challenges to its approval.

The institute says Japan has been the world's fastest aging country, and with its birthrate among the lowest, its population decline would be among the deepest globally in coming decades.

Experts say that Japan's population will keep losing 1 million every year in coming decades and the country urgently needs to overhaul its social security and tax system to reflect the demographic shift.

"Pension programs, employment and labor policy and social security system in this country is not designed to reflect such rapidly progressing population decline or aging," Noriko Tsuya, a demography expert at Keio University, said on public broadcaster NHK. "The government needs to urgently revise the system and implement new measures based on the estimate."